The present invention relates generally to an ergonometric moveable support arm used for computer peripheral equipment, e.g. a mouse or keyboard, and, more particularly, to a support arm with a controlled vertical bias which provides greater stability and adjustable spring loads.
A floating moveable arm supports is now available for providing an upward bias to the user's arm in order to overcome some of the effects of gravity while performing tasks of long duration. One such support is shown in FIGS. 1-3 whose constructional details are described below. To provide a cradle that moves with the user's arm and continually provide an upward bias thereagainst, an upward spring load can be arranged at each side of the cradle as seen in FIGS. 4 and 5 also discussed in greater detail below. With such an arrangement, however, the system becomes unstable if the arm weight is not uniformly distributed to each spring and all the load shifts to only one of the springs. In practice, such uniform distribution is often not achieved. Non-uniform arm weight distribution also causes the yoke to bind in the cradle with consequent unacceptable results. Another disadvantage of this approach is that the upward biasing force changes with the vertical displacement based on the spring rate. Moreover, each cradle assembly is manufactured with a particular spring load that cannot easily be changed by the user. Thus, if the cradle force is too high or too low, a new cradle assembly must be installed at much additional cost.
Counterbalancing mechanisms are known which utilize a torsion bar and cam arrangement for providing positive control for heavy container lids. One such torque-bar counterbalance mechanism is shown in Design News, Nov. 4, 1985. This mechanism is designed, however, for more complex applications on which elaborate covers are employed and in which it is necessary to determine the center of gravity and its path, and a dynamic nomograph or computer is used to correlate the wide variety of cover possibilities with the possible counterbalancing mechanisms. In addition, a positively locking vernier gear is provided to fine-tune the balancing by manipulation of multiple gear meshes. Although such a mechanism may be suitable for heavy lids and covers, it is too complex and expensive for arm supports of the type to which the present invention is directed.
It is an object of the present invention to provide an arm support which is both simple in construction and inexpensive to produce while producing a constant or uniform upward biasing reaction force.
It is a further object of the present invention to permit the substitution of different cradles in an economic manner to obtain different magnitudes of uniform upward force in accordance with the user's comfort.
It is still a further object of the present invention to achieve stability of the cradle and thereby allow tilting of the cradle to comply with natural arm movements without binding the yoke within the cradle.
I have found that the disadvantages associated with known devices for arm support can be overcome and the above-stated objects achieved by configuring the yoke with cam surfaces. In particular, in one embodiment of the present invention, four grooved followers in the form, for example, of two sets of opposed wheels made of Nylon, Teflon or the like are arranged within the cradle housing and ride along cam surfaces on each side of a U-shaped yoke as the cradle housing moves relative to the yoke. A set of two followers is provided to engage cam surfaces and is arranged at each side or leg of the yoke. The followers are normally biased toward one another onto the cam surfaces by a coiled tension spring. Movement of the followers on both sides of the yoke is controlled by two rotatable crank rods which extend between the yoke legs, thereby providing system stability to avoid binding of the yoke within the cradle as the user's arm undergoes tilting movements.
Another feature of the present invention resides in that the configuration and size of the cam surfaces on the legs of the yokes can be varied to obtain constant or uniform upward reaction forces of different magnitudes in accordance with the user's comfort.
In another embodiment of the present invention, the cam surfaces on the yoke can be provided with a notch to restrict, where desired along the path of relative movement between the cradle housing and yoke, vertical movement of the cradle while still permitting the cradle housing to pivot and tilt.